Commonly assigned Canadian Patent 2,855,417 published Jan. 4, 2015 and WO 2016/000068 A1 (corresponding to CA 2,885,146 published Jan. 2, 2016), each of which is expressly incorporated herein by reference in their respective entireties, teach various procedures to exploit induced fractures in multi-fractured horizontal wells, used for, but not limited to, the improved production of oil from tight reservoirs or any consolidated reservoir matrix.
CA '417 and '146 teach the utilization of the fractures as injection or production conduits attached to a horizontal well so that injection fluids can be selectively distributed in a continuous manner to alternate fractures with the remaining fractures employed as production fractures. By eliminating communication between injection and production fractures within the horizontal wellbore, injected fluids are forced to flow through the reservoir matrix from the injection fractures to the production fractures.
One embodiment taught in the above publications teaches the use of a long tubing from the surface running through an isolation actuatable packer placed between the two fractures nearest the toe of the horizontal well. Injectant, which could be but is not limited to water, hydrocarbon gas, CO2 or mixtures thereof, is conveyed continuously down the long tubing and enters the fracture furthermost from the heel of the horizontal well (i.e. at the toe thereof) and penetrates the formation matrix pushing oil towards the adjacent fracture in the direction of the heel and thence into the annulus of the horizontal well, whence it is conveyed to the surface. Once the injectant appears at the surface in sufficient quantity, the packer is deactuated and is moved one fracture closer to the heel of the horizontal well where it is actuated and continuous injection is resumed. The process continues until the entire reservoir volume delineated by the fractures has been flooded with the injectant. This process has modest cost, but suffers from only a single segment of the reservoir being flooded at one time.
CA 417' and '146 also teach the use of dual-channel tubing or pipe placed in the well liner and having independent flow areas, for example a single tubing or pipe with an internal divider that that creates independent internal channels or a concentric tubing or pipe having a central channel and an annular channel. The tubing or pipe contain apertures proximate each fracture and an isolation packer around the tubing or pipe between each fracture to prevent communication between the channels within the wellbore. In a continuous process, injectant is conveyed into approximately alternate fractures and oil produced from the other fractures. Being continuous, this process produces higher oil rates, but also has higher capital costs because of the need for specialized tubing or pipe.
Given the current extremely low oil price (<$30/bbl) and the high cost of drilling and multi-fracturing long and deep horizontal wells (approximately $8-million/well) there is a need for a process with low capital cost that can revive existing multi-fractured wells. The rapid decline rate in tight light oil reservoirs such as the Bakken and Eagle Ford wells can be 70% in the first year and 50% in the second year, however, given sufficient secondary oil recovery, companies could cease drilling new wells without a fall in overall oil production. These existing wells are largely past their 2-year primary recovery prime, however 90-95% of the original oil-in-place is still there.
Other than Fracture Flooding™, as described in the above-referenced documents, the prospects for secondary oil recovery in light tight oil reservoirs are bleak. Some operators have attempted water flooding or gas flooding from parallel multi-fractured wells, however, communication between fractures short-circuits the flow patterns, undermining reservoir sweep efficiency. Re-fracturing is expensive and has provided inconsistent results. The process of the present invention holds promise to solve all the major economic and engineering problems concerning secondary oil recovery from light tight oil reservoirs: low capital cost, higher and sustained oil production rates and higher oil recovery factor.